Systematic Calibration of Pourbaix Diagrams of Organic Molecules

A systematic calibration methodology of the theoretically estimated Pourbaix diagrams (PD) of organic molecules is presented. This methodology considers the availability of experimental data and can be used when one or more data are available. Nitrogen-based systems were considered to illustrate this methodology, specifically methylene blue, bipyridine, and benzidine. The calibration scheme can be used to calculate derivatives obtained by functionalization of the organic cores and can be easily extended to other organic families. Results are based on DFT calculations and the linear approximation of PD. Performance of different functionals and basis set combinations is considered and discussed. We show that several values reported in the literature for the free energy of the proton and the redox potential of the standard hydrogen electrode can be considered in a systematic way to improve the prediction of PD. Different approximation schemes were compared.